C-shaped magnetizable core

ABSTRACT

A C-SHAPED MAGNETIZALE CORE AND METHOD OF MAKING SAME OF POWDERED MATERIAL MANUFACTURED BY FILLING A PREDETERMINED QUANTITY OF THE POWERED MATERIAL INTO A C-SHAPED MOLD HAVING TWO ENDS AND HAVING A TRAPEZOIDAL CROSS SECTION, COMPRESSING SAID POWDERED MATERIAL TO A DENSITY OF AT LEAST 6.0 G./CM.3 BY A COOPERATING, C-SHAPED RAM FROM THE LARGER TRAPEZOIDAL BASE TOWARD THE SMALLER TRAPEZOIDAL BASE, WITHDRAWING THE RAM AND EJECTING THE CORE FROM THE DIE WITH A COMPARABLY C-SHAPED ROD FROM THE SMALLER TRAPEZOIDAL BASE TOWARD THE LARGER TRAPEZOIDAL BASE, THE CORE UNIFORMLY EXPANDING LATERALLY AS IT IS EJECTED FROM THE DIE HAVING A UNIFORM DENSITY OF IMPROVED STRUCTURAL, MAGNETIC AND ELECTRICAL PROPERTIES.

R. B. GRAF ETAL.

C-SHAPED MAGNETIZABLE CORE Feb. 23,1971 f 2 Sheets-sheaf;

EiledMay 1, 1969 2o FIG. 2.-

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III I I N VEN TORS. EDWARD H. CH4 N7 JR.

RICHARD B. GRAF 8 JOHN F. MARCO WA-JP g Attorney United States PatentOlfice US. Cl. 336-233 4 Claims ABSTRACT OF THE DISCLOSURE A C-shapedmagnetizable core and method of making same of powdered materialmanufactured by filling a predetermined quantity of the powderedmaterial into a C-shaped mold having two ends and having a trapezoidalcross section, compressing said powdered material to a density of atleast 6.0 g./cm. by a cooperating, C-shaped ram from the largertrapezoidal base toward the smaller trapezoidal base, withdrawing theram and ejecting the core from the die with a comparably C-shaped rodfrom the smaller trapezoidal base toward the larger trapezoidal base,the core uniformly expanding laterally as it is ejected from the diehaving a uniform density of improved structural, magnetic and electricalproperties.

BACKGROUND OF THE INVENTION The utilization of high permeabilitymaterial such as powdered molybdenum iron-nickel alloy in the cores ofloading coils has been long known in the communications industry. Suchmaterials are conventionally compressed at extremely high pressures suchas 100' to 150' tons per square inch and then annealed to improvemagnetic and structural properties, and then insulated as by varnishcoating and then baking. One piece cores have been made in fulltorroids, however, that shape presents several disadvantages in theindustry. By virtue of its single surface construction, the torroidalcore requires any coil being placed around the core to be wound directlyabout the shape. Thus, any insulation required between the winding andthe core material must be either placed on the winding or coateddirectly on the torroid which further necessitates special handling ofthe winding and the core to prevent damage to the insulation.Additionally, there are limitations to the winding of a coil around thecore in that automatic winding on such a shape is difficult, and in thecases of a heavy conductor, is impossible thereby necessitating handwinding. In order to circumvent these manufacturing problems, cores havebeen made in L shapes with two of these shapes subsequently assembled toform torroidal cores. It has been necessary in the past in makingsectional cores to employ a molding die made up of a plurality ofremovable die sections in order to permit withdrawal of the formed Lfrom the die cavity. The die sections forming the L-shaped cavityconventionally are individually clamped on a suitable platform in anabutting sort of relationship and after the required pressure has beenapplied to a charge of powdered material within the cavity the diesections are unclamped from the platform and moved away from the formedbody to permit removal of the compressed core. Both the core sectionshape and the method of making that shape present serious disadvantageswhich are overcome by the shape and method of manufacture of myinvention.

3,566,323 Patented Feb. 23, 1971 The necessity of repetitive clampingand unclamping of the plurality of die sections in the forming operationfor L shapes results in rapid deterioration of the die sections whichfurther results in varying core shapes. Further, the occurrence of gapsbetween the sections upon reassembly for another molding contributes tofurther nonuniformity of the shape of the product formed therein. Theability of the die sections to be disassembled contributes tonon-rigidity of the combined shape and allows non-uniform compression ofthe charge of powdered material within the cavity under the highcompressing pressures. Non-uniform compression results in a non-uniformdensity of material, an irregular shape, as well as internal stresseswithin the material, all of which contribute to further disadvantages.The necessity of unclamping and clamping the die sections to remove theformed core and to prepare for another compression does not lend to anysort of automatic operation of manufacture.

SUMMARY OF THE INVENTION The present invention generally provides amethod for forming a C-shaped, trapezoidal cross-section of a core ofcompressed powdered material by uniformly subjecting the powderedmaterial contained in a die cavity to a uniform high pressure and ofuniformly releasing the pressure following the compression and ofremoving the formed section of compressed powdered material from thepressure cavity in such a manner to avoid flexure or deformation of thebody during the removal. In particular the present invention includes amethod for forming C- shaped sections of cores in an automatic operationhaving a cavity surrounded by a unitized die structure symmetric aboutone central axis. The cores produced by the method of the presentinvention are of more uniform density, permeability and physicaldimension and possess improved magnetic, electrical and structuralcharacteristics. Additionally, the novel shape of the core from theunitized die structure exhibits more uniform magnetic and electricalcharacteristics in a torroidal combination with another section. Thesectional C-shaped cores are capable of receiving machine wound coils ofconductors of no special size limitations, wound on a core form andinsertable over the legs of the sections as they are assembled. Further,in assembled relation the juncture between the sections falls Within thephysical limits of the core Winding, thus minimizing any non-uniformityof magnetic field distribution which might exist in that juncture. Theseand other features of the present invention will appear more fully fromthe following detailed description and drawings which accompany thespecification.

DESCRIPTION OF THE DRAWINGS -FIG. 1 is a partial plan view showing dieconstruction for making C cores.

FIG. 2 is an elevational view partially in section illustrating dieapparatus for performing the invention.

FIG. 3 is a side elevation of a C core of the invention.

FIG. 4 is a front elevation of the C core of the invention.

FIG. 5 is a plan view of the C core of the invention.

FIG. 6 is an elevation of a torroid formed of C cores of the invention.

FIG. 7 is a plan view of a torroid formed of C cores of the inventionincluding windings.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsreference numeral 2 indicates a die sleeve having die inserts 4a and 4bof a hard material such as a carbide and a table 6 upon which inserts 4and 4b are seated, all of which form unitized die structure 7. Dieinserts 4a and 4b form a C-shaped die cavity 8 having a top opening 10and bottom opening 12. Tapered walls 13 give the cavity 8 a trapezoidalcross-section with walls 13 being the non-parallel sides. Table insert 6has an opening 14 to receive an ejector 16 having a C-shaped portion 18adapted to cooperate with opening 12. In the example disclosed inserts4a and 4b and table 6 are retained in sleeve 2 by a shrink fit. Thesleeve 2 is adapted to be received into automatic stamping equipment,not shown but well known in the industry, which operates ejector 16 atappropriate intervals and in which also is mounted actuating means forcompressing punch 20 having a C-shaped portion 22 adapted to cooperatewith opening 10 for compressing material placed in the cavity 8 of thedie. In the pre ferred arrangement table -6 meets die molding insert 4forming a shoulder 24 in the vicinity of opening 12. With such anarrangement ejector 16s outer perimeter describes an envelope smallerthan die opening 8. It is to be noted, however, that shoulder 24 andejector 16 in the retracted position as shown by the dotted line of FIG.2 form the bottom of cavity 8, against which the compression of ram 20is developed.

Referring now to FIGS. 3, 4 and 5, reference numeral indicates amagnetizable C-shaped core having a trapezoidal cross-section formed byparallel bases 32 and 34 being the upper and lower bases, respectively,and by non-parallel sides 36. It is to be noted that both the arms 38 ofthe C-shaped and the connecting portion have a trapezoidal cross-sectionas well as the overall crosssection illustrated by the end view in FIG.3.

FIGS. 6 and 7 illustrate the use of two C-shaped cores 30 in a coilapplication wherein legs 38 of each of the Cs are joined but one of thecoils is inverted with respect to the other such that the compositetorroid 39 formed by the two cores 30 has parallel bases 40 and 42 whichare co-planar with bases 32 and 34. FIG. 7 also illustrates torroid 39having a coil form 44 and a winding 46 wound thereon surrounding legs 38of the composite cores 30. It is to be noted that any air gap that mightexist between the two composite cores within the juncture of legs 38 iswell Within the internal field of the windings 46 surrounding legs 38.

To manufacture C-shaped magnetizable cores the die structure shown inFIG. 1 and 2 may be installed in the stations provided in automaticpressing machines for compressing insulated powdered material as is wellknown in the industry. Such a machine would perform particularmechanical functions, such as introducing the measured quantity ofpowdered metal into the die cavity, initiating the actuating mechanismto compress the material into an integral core and further initiatingthe ejecting action to remove the core from the molding die. Thespecific sleeve 2, punch 20 and ejector 16 may be adapted to be receivedin the appropriate cooperating sections of such automatic machinery. Thecommencement of the manufacturing operation occurs with lubrication ofthe die mold walls 13, as by an atomized lubricant followed by theintroduction of a measured quantity of powdered material into the cavity8. Following this the automatic machinery, not shown, initiates thedownward thrust of the punch 20 so that the C-shaped portion 22 entersthe die mold cavity 8 at oepning 10 contacting the powdered material.The

area and shape of the C-shaped compressing face 23 of punch 20 isslightly less than opening 10, however, it closely approaches that ofcavity 8 at the maximum downward stroke of punch 20. This is due to thetaper of the side walls 13, which in the example is 1 from the vertical.This insures that the compressive stroke at the downward extent providesa uniform compacting action within the cavity such that the materialthroughout the cross section of the core is uniformly compacted. Sincethe walls 13 of the cavity 8 are only slightly tapered and since thecorners formed by the meeting of punch 20 and the walls 13 in the baseformed by shoulder 24 and the ejector 1-6 are substantially squared, auniform compression exists throughout the cross section at the instantof maximum compression.

In the example disclosed, a core of insulated powdered material isproduced having a uniform high permeability throughout. The uniformityof permeability is achieved through the uniform compression and absenceof additional stresses in the form due to fluctuations in the die. Highpressures may be used to achieve the higher permeabilities to compressthe core because of the core and die geometry. Cores exhibitingpermeabilities of 100 to 350 may be pressed under pressures of to 150tons/ square inch in the shape and die of the invention. Cores thuspressed from insulated powdered metal such as the nickel-iron alloyshaving at least 30% nickel, commonly known as the permalloys, exhibit auniform density of about 7.0 to 8.75 g./cm. Such cores of insulatedpowder may be produced of base alloys including up to nickel in the basealloy and may also include additions of one or more of copper, cobalt,chromium, molybdenum and silicon as is well known in the art. Further,cores of a powder alloy containing at least 80% iron, 8% silicon and 4%aluminum have been pressed in C-shapes of uniform density of about 6.0at pressures of about tons and having a permeability of about 200.Uniform compression equalizes the distribution of forces throughout thecore thereby minimizing the development of local stresses within thecore structure, which minimizes deterioration of the magnetic andelectrical properties of the core.

Upon completion of the compression stroke, punch 20 is removed fromopening 8 thus clearing the way for the ejection of the core 30 from thedie cavity 8. The ejection is initiated by ejector 16 being moved by theautomatic equipment, not shown, in an upward direction. Due to thetrapezoidal cross-section in all aspects of the C- shaped mold discussedabove, as soon as core C is raised in the cavity 8 its side walls 36clear the side walls 13 of the mold at a uniform rate. The ability ofthe core 30 to expand equally in all directions as it is ejected fromthe mold further minimizes any stresses or non-unformities in densitythat might be developed within the core if it were otherwise ejectedfrom the mold.

Referring now to FIGS. 6 and 7 a torroidal core is shown formed by twoC-shaped cores with their legs 38 in abutting relationship. Theillustration shows one of the two cores in an inverted condition withreference to the other such that the ends 38a of the legs are injuxtaposed relation minimizing any air gap which might otherwise occur.It will be further noted that this juncture of leg 38 occurs well withinthe field of the winding 46 forming an integral part of a coil. Thejuncture of the two L sections would fall outside the coil 46 allowing adeterioration in the uniformity of the field strength which wouldotherwise occur within the core in coil combination. Since the windings46 may be wrapped around a form 44 which may serve as an insulator, thesteps necessary to insulate a solid torroidal core may be avoided.Additionally, the coils may all be machine wound on the form 44,including heavy conductor 'windings. Thus, the invention contributessubstantially to the automation of manufacture of wound cores.

We claim:

1. A magnetizable core of compressed powdered material comprising acenter section, two parallel leg sections extending substantiallyperpendicularly to the ends of said center section forming a C-shapedcore, said center section and said leg sections having a substantially 6trapezoidal cross-section, the parallel bases of which form 4. Amagnetizable core according to claim 3 having a the C-shaped sides ofsaid core. density of at least 6.0 g./cm.

2. A magnetizable core according to claim 1 of compressed insulatedpowder material and from the group References Cited consisting ofnickel-iron base alloys containing at least 5 UNITED STATES PATENTS 30%nickel and iron-silicon-aluminum alloys containing at least 80% iron, atleast 8% silicon and at least 4% alummum' 2,508,705 5/1950 Beller et a1336233X 3. A magnetizable core according to clalm 2 wherein 3,43012/1969 Eyberger 336 233X the nickel-iron alloy includes at least one ofcopper, cobalt, 10 Chromium, molybdenum and Silicoll- THOMAS J. KOZMA,Primary Examiner

